Apparatus for analyzing coherent radiation

Abstract

Apparatus for detecting the presence and/or determining the intensity and/or determining the wavelength and/or determining the threshold direction of coherent radiation in the presence of incoherent ambient radiation. A preferred form of apparatus includes a Fabry-Perot etalon having three regions of different thickness such that the optical phase difference between the second region and third adjacent region is less than π and the optical phase difference between the first and second regions is substantially greater than the optical phase difference between the second and third regions; the etalon having a first surface positioned to receive coherent radiation and a second surface, the average distance between the surfaces being such that the optical path difference between transmitted portions of radiation impinging on the first surface is substantially greater than the coherence length of the coherent radiation; said etalon being modulated with respect to the source of coherent radiation; elements for detecting radiation transmitted through each of the regions and for generating separate first, second and third signals, respectively responsive to the radiation leaving each of the regions, elements for detecting the phase difference between the detected signals, and elements for determining the wavelength of the coherent radiation corresponding to the detected phase differences.

What is claimed is: 
     
       1. Apparatus for determining the wavelength of coherent radiation in a range of wavelengths to be monitored in the presence of incoherent ambient radiation comprising: a Fabry-Perot etalon having three regions of different preselected thicknesses corresponding to said range of wavelengths such that the optical phase difference between the second region and third adjacent region is less than π for any given wavelength in said range and the optical phase difference between the first and second regions is substantially greater than the optical phase difference between the second and third regions;   said etalon having a first surface positioned to receive coherent radiation and a second surface, the average distance between said surfaces being such that the optical path difference between transmitted portions of radiation impinging on said first surface is substantially greater than the coherence length of the noncoherent radiation but substantially less than the coherence length of the coherent radiation;   means for modulating said etalon with respect to a source of coherent radiation;   means for detecting radiation transmitted through each of said regions and for generating separate first, second and third signals, respectively responsive to the radiation leaving each of said regions;   means for detecting the phase difference between the signals detected from the second and third regions to determine the broad range of desired wavelength, and means for detecting the phase difference between the signals detected from the first and second regions within the broad range detected; and   means for determining the wavelength of the coherent radiation corresponding to the detected phase differences.   
     
     
       2. Apparatus according to claim 1 further comprising means for detecting the presence of coherent radiation. 
     
     
       3. Apparatus according to claim 1 further comprising means for determining the intensity of coherent radiation. 
     
     
       4. Apparatus according to claim 1 further comprising means for determining the threshold direction of coherent radiation. 
     
     
       5. Apparatus according to claim 1 further comprising means for subtracting a non-coherent radiation component from the coherent radiation component in said first, second and third signals, respectively. 
     
     
       6. Apparatus according to claim 5 wherein said means for subtracting non-coherent radiation comprises; a plane window forming a fourth region;   means for detecting radiation transmitted through said fourth region and generating a fourth signal responsive to the radiation leaving said fourth region; and   means for subtracting said fourth signal from said first, second and third signals, respectively.   
     
     
       7. Apparatus according to claim 6 further comprising low frequency filters for reducing the low frequency background incoherent signals from the output of each of said means for detecting radiation, respectively. 
     
     
       8. Apparatus according to claim 6 further comprising means for subtracting said fourth signal from said second and third signals to produce a signal indicative of the presence of coherent radiation. 
     
     
       9. Apparatus according to claim 8 further comprising: a plane window forming a fifth region;   means for detecting radiation transmitted through said fifth region and for generating a fifth signal responsive to the radiation leaving said fifth region; and   means for filtering out the non-coherent radiation component from said fifth signal and for determining the pulse width and intensity of the resultant coherent radiation in a wavelength range corresponding to preselected characteristics of said means for detecting radiation transmitted through said fifth region.   
     
     
       10. Apparatus according to claim 1 wherein at least one of said means for detecting the radiation transmitted through its corresponding region has four detecting elements disposed in quadrant relationship, and means for determining the threshold direction of the coherent radiation responsive to the relationship of the detected radiation incident on each of said elements. 
     
     
       11. Apparatus according to claim 1 wherein said means for detecting the radiation transmitted through said first region has four detecting elements disposed in quadrant relationship, and wherein said means for detecting the radiation transmitted through said second region has four detecting elements disposed in quadrant relationship, and means for determining the threshold direction of the coherent radiation responsive to the relationship of the detected radiation incident on each of said elements. 
     
     
       12. Apparatus according to claim 1 further comprising: a plane window forming a fourth region;   means for detecting radiation transmitted through said fourth region and generating a fourth signal responsive to the radiation leaving said fourth region;   means for subtracting said fourth signal from said first signal and for detecting the phase of the resultant coherent radiation of the first region;   means for subtracting said fourth signal from said second signal and for detecting the phase of the resultant coherent radiation of the second region;   means for subtracting said fourth signal from said third signal and for detecting the phase of the resultant coherent radiation of the third region;   means for detecting the phase difference between the second and third regions to determine the broad range of desired wavelength and means for detecting the phase difference between the first and second regions within the broad range detected; and   means for determining the wavelength of the coherent radiation responsive to the phase difference detected between the first and second regions.   
     
     
       13. Apparatus for detecting the presence and determining the threshold direction of coherent radiation in the presence of incoherent ambient radiation comprising: a Fabry-Perot etalon having two regions of different thickness such that there is an optical phase difference therebetween;   said etalon having a first surface positioned to receive coherent radiation and a second surface, the average distance between said surfaces being such that the optical path difference between transmitted portions of radiation impinging on said first surface is substantially greater than the coherence length of the incoherent radiation; but substantially less than the coherence length of the coherent radiation   means for modulating said etalon with respect to a source of coherent radiation;   a first plane window;   a second plane window;   means for detecting radiation transmitted through said etalon regions and through each of said windows, and generating separate first, second, third and fourth signals responsive to the radiation leaving said etalon regions and windows, respectively;   means for subtracting said third signal from said first and second signals to produce an output signal indicative of the presence of coherent radiation; and   means for filtering out the non-coherent radiation from said fourth signal and for determining the intensity of the resultant coherent radiation in a wavelength range corresponding to preselected characteristics of said means for detecting radiation transmitted through said second window.   
     
     
       14. Apparatus according to claim 13 wherein said means for detecting the radiation transmitted through said etalon has four detecting elements disposed in quadrant relationship, and means for determining the threshold direction of the coherent radiation responsive to the relationship of the detected radiation incident on each of said elements. 
     
     
       15. Apparatus for detecting the presence, determining the intensity, determining the wavelength in a range of wavelengths to be monitored and determining the threshold direction of coherent radiation in the presence of incoherent ambient radiation comprising, in combination: a Fabry-Perot etalon having three regions of different preselected thicknesses corresponding to said range of wavelengths such that the optical phase difference between the second region and third adjacent region is less than π for any given wavelength in said range and the optical phase difference between the first and second regions is substantially greater than the optical phase difference between the second and third regions;   said etalon having a first surface positioned to receive coherent radiation and a second surface, the average distance between said surfaces being such that the optical path differences between transmitted portions of radiation impinging on said first surface is substantially greater than the coherence length of the incoherent radiation, but substantially less than the coherence length of the coherent radiation   means for modulating said etalon with respect to a source of coherent radiation;   a plane window forming a fourth region;   a plane window forming a fifth region;   means for detecting radiation transmitted through each of said regions and for generating separate first, second, third, fourth and fifth signals, respectively responsive to the radiation leaving each of said regions;   means for subtracting said fourth signal from said second and third signals to produce an output signal indicative of the presence of coherent radiation;   means for filtering out the non-coherent radiation from said fifth signal and for determining the pulse width and intensity of the resultant coherent radiation in a wavelength range corresponding to preselected characteristics of said means for detecting radiation transmitted through said fifth region;   means for subtracting said fourth signal from said first signal and for detecting the phase of the resultant coherent radiation of the first region;   means for subtracting said fourth signal from said second signal and for detecting the phase of the resultant coherent radiation of the second region;   means for subtracting said fourth signal from said third signal and for detecting the phase of the resultant coherent radiation of the third region;   means for detecting the phase difference between the second and third regions to determine the broad range of desired wavelength, and means for detecting the phase difference between the first and second regions within the broad range detected;   means for determining the wavelength of the coherent radiation responsive to the phase difference detected between the first and second regions;   said means for detecting the radiation transmitted through said first region having four detecting elements disposed in quadrant relationship;   said means for detecting the radiation transmitted through the second region having four detecting elements disposed in quadrant relationship;   means for detecting radiation incident on each of said elements; and   means for determining the threshold direction of the coherent radiation responsive to the relationship of the detected radiation incident on each of said elements.